1. Field of the Invention
The present invention relates to an apparatus for the collection and distribution of liquid in a column. In this a plurality of unordered or ordered packings are located in the column in each case on a carrier grid, beneath which the apparatus for the collection and distribution of liquid is arranged.
2. Description of the Prior Art
In material exchange columns of this kind the packing or the filling body is supported by a carrier grid, with the liquid dripping off over this carrier grid and being caught, mixed and conducted to the new distribution or redistribution respectively or to the liquid removal.
Field of application is preferably the material separation technique such as the absorption and desorption in fluid systems, the distillation and rectification and the technical carrying out of reactions at catalyst layers. For several years it has been usual to use non ordered filler bodies or packings, in particular structured or ordered packings respectively, in material exchange columns. Their effectiveness depends very strongly on the uniform wetting of their surface with back-flowing liquid and on the observing of a liquid-vapour mass ratio which is the same over the cross-section. In the event of non-uniform liquid output and distribution and the resultant non-uniform wetting, maldistribution (faulty distribution) arises inside the filler body layers for example in the form of passage flow. This quite considerably restricts the effectiveness and the function of the exchange column.
For this reason a liquid distributor is arranged above a packing section which is intended to distribute the downwardly flowing fluid as homogeneously as possible over the column cross-section.
A large number of collector and distributor apparatuses for liquids are known which attempt with more or less cost and complexity to achieve the required uniform liquid distribution in the described material exchange columns. Distributors of this kind are for example known from an article by P. Bomio et al., Chem. Tech., vol. 43, no. 11/12, 1991 and are designated there as tube distributors, element distributors or passage distributors. These types of liquid distributors have horizontally oriented distributor passages which are fed by at least one main passage, which as a rule extends perpendicularly to the distributor passages. In a tube distributor the distributor passages are closed at the upper side; in an element distributor or passage distributor they are open above. Element distributors or passage distributors operate with a certain filling level in the passages. The hydrostatic pressure which is connected therewith regulates the liquid amount which drips through special flow-off elements onto the packing section lying below them. The filling height increases approximately as the square of the liquid load. Since the passages cover over a large portion of the column cross-section, a distributor of this kind contains large amounts of liquid of a specific composition. This affects the inertia of the distributor and thereby of the entire column with respect to rapid changes of the composition of the distributed liquid.
The description of the functioning principles of these known collector and distributor apparatuses also illustrates their disadvantages to the same extent.
The liquid flowing out of this packing section is caught and brought together by a liquid collector. The liquid is conducted out of the liquid collector into the main passage or the side passages of the distributor via a tube or shaft construction. The feeding in takes place via a relatively large, generally central inflow or a plurality of relatively large inflows. The turbulences and flow velocities resulting from this method of construction are very large in distributor inflows of this kind. For this, suitable means, such as a pre-distributor passage or an inflow calmer, must be installed in the main passage. The transfer of the liquid takes place in one stage or in a plurality of stages in a closed or open design, however always in the form that the liquid flows following gravity. In this the problem arises that a non uniform distribution of the liquid is produced by the flow in the longitudinal direction of the distributor passages. Depending on how far the liquid inflow and the liquid outflow are separated from one another in a passage, the outflow opening is flowed through by liquid with different outflow speed.
It was also recognised that the weak points of the material exchange column with respect to rapid load changes lie at the liquid collectors and liquid distributors. Particularly important are those distributors and collectors which are arranged between packing sections and which are intended to provide for as uniform a distribution of the back-flowing liquid as possible over the column cross-section. It takes for example a long time until a new stationary state, in conjunction with a higher or lower filling level in the distributors, is achieved. The cause is to be seen in that the concentration of large liquid volumes must be changed before the new stationary state sets in.
Furthermore, it must be remarked that the previous apparatuses for the bringing together and complete mixing of the entire back-flowing liquid after their being caught in the collector and the subsequent multiple new distribution or redistribution up to and including the fine distribution at the drip points are constructionally very complicated and expensive.
The frequently used multiple stage coarse distribution of the entire back-flowing liquid through inflows, main passages and side passages contains many sources for a maldistribution of the liquid. Sources of error are for example the non uniform flow conduction through continual accelerations and decelerations of the liquid and the insufficient levelling during the assembly.
In the known apparatuses, large geodetic height differences are required to sufficiently accelerate and decelerate large liquid volumes a plurality of times. Through this the constructional height of the know apparatus is relatively large.
In addition the apparatuses for the coarse distribution cause a strong non uniformity for the gas or vapour flow respectively, which has an influence on the efficiency of the entire column.
From the prior art it is further known that one can dispense with installations for the intentional mixing of the downwardly dripping and captured liquid in order to reduce the constructional height of the material exchange columns. An apparatus for the collection and redistributing of liquid in accordance with the preamble of the invention was described in U.S. Pat. No. 5,464,573. The apparatus disclosed therein dispenses with installations for the intentional mixing of the captured liquid with the decisive disadvantage that in the event of a non uniform distribution of the liquid a liquid equalization and the flows connected therewith come about in the horizontal plane. The already described effects of turbulences in the liquid distribution in the conventional distributor apparatuses are even increased through the simple saving in collection and pre-distributor stages and the result is non uniform liquid outflow out of the distributor.
The object of the present invention is now to develop an apparatus for the collection and distribution of gas and liquid in material exchange columns which enables a very homogeneous liquid output over the column cross-section with a low constructional height and which in addition enables a rapid adaptation to load changes during operation.
An apparatus in accordance with the present invention is designed in such a manner that the liquid collector, the gas or vapour distributor respectively and the liquid distributor are combined with one another in one apparatus.
The back-flowing liquid which is caught by a collector which is modified in accordance with the present invention is not intentionally brought together and intensively mixed for the purpose of an equalization of the composition, but rather it was surprisingly found that the object of the present invention is satisfied in that the liquid is distributed directly in the collector to such a uniform extent that a hydrodynamic equalization is realized with a small geodetic height difference.
A hydrodynamic equalization is present when at spatially separated similar liquid outlet openings the direction, velocity and surface level of the liquid flow lying above them are equal.
The intensity of the equalization flows and the amount of the liquid which participates in the hydrodynamic equalization is influenced by the hydrodynamic maldistribution at the end of the packing section which is located above the collector and distributor apparatus. The collector and distributor apparatus has flow splitters which conduct the horizontal equalization flows in such a manner that they can exert no disturbing influence on the new distribution of the back-flowing liquid. The apparatus is designed in such a manner that the liquid preferably flows directly from the collection location to the nearest lying drip point with a low flow velocity.
To be named as essential advantages of the invention are that a very homogeneous fluid dynamical liquid output with high distribution quality is achieved through the reduction of unnecessary flow turbulences and a high drip location density is realized with a small constructional height. The equalization flows required are far less than the flows in previous collector and distributor constructions.
Furthermore, the stationary liquid content (hold up) is reduced in comparison with a conventional collector and distributor apparatus through a lower number of distributor stages and the horizontal liquid transport is strongly reduced. Smaller passage widths can thus be realized for the distributor passages.
An improvement of the load change behaviour is caused by the shorter dwell time of the liquid in the collector and distributor apparatus and through the reduction of the stationary fluid content.
Advantageous is also the reduction of the total weight of the apparatus and the reduction of the cost and complexity of the assembly in comparison with conventional collector and distributor apparatuses.
Instead of the reduction of the constructional height of the column, the separator stage number can subsequently be increased in existing columns when the possibility of the installation of additional packings after the replacement of the conventional collector and distributor apparatus with a novel one in accordance with the invention is used.